Method of dehydrating magnesium chloride powder

ABSTRACT

THIS INVENTION RELATES TO A MAGNESIUM CHLORIDE DEHYDRATING METHOD AND TO APPARATUS FOR PRACTICING THE INVENTION. A STREAM OF MOLTEN SALTS CONTAINING MAGNESIUM CHLORIDE IS CARRIED BY A LAUNDER AND SOLID PARTICLES OR POWDER OF MAGNESIUM CHLORIDE, HAVING SOME WATER THEREIN, IS DISCHARGED UPON THE STREAM, THE HEAT OF THE STREAM CAUSING THE WATER TO BE FLASHED OFF AS STEAM. THE STEAM IS WITHDRAWN AND THE DEHYDRATED POWDER IS THEREAFTER RAPIDLY MIXED WITH AND MELTED BY THE MOLTEN STREAM AS IT IS DISCHARGED INTO A CLOSED BATH.

Feb. 23.,l 1971 R, M WHEELER 3,564,722

METHOD OF DEHYDRATING MAGNESIUM CHLRIDE POWDER Filed Feb. 24, 1969 Q WMM ATTORNEYS United States Patent Olce 3,564,722 METHOD OF DEHYDRATING MAGNESIUM CHLORIDE POWDER Roger M. Wheeler, Tulsa, Okla., assignor to American Magnesium Company, rIulsa, Okla., a corporation of Delaware Filed Feb. 24, 1969, Ser. No. 801,476 Int. Cl. F26b 3/00 U.S. Cl. 34-9 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a magnesium chloride dehydrating method and to apparatus for practicing the invention. A stream of molten salts containing magnesium chloride is carried by a launder and solid particles or powder of magnesium chloride, having some water therein, is discharged upon the stream, the heat of the stream causing the water to be flashed off as steam. The steam is withdrawn and the dehydrated powder is thereafter rapidly mixed with and melted by the molten stream as it is discharged into a closed bath.

BACKGROUND AND SUMMARY OF THE INVENTION A method of manufacturing magnesium metal includes the electrolysis of molten magnesium chloride in a cell, the chlorine being taken at one electrode and the magnesium metal at the other. One of the most diicult problems, however, in connection with this method is that of producing magnesium chloride having a suiciently low water and magnesium oxide content to achieve eicient and economic operation of the cell. Magnesium chloride easily combines with water and the separation of the water from the chloride without degradation thereof is difficult. A widely used method of separating the water is by heating magnesium chloride to evaporate off the water but this is dicult to accomplish without causing a reaction producing magnesium oxide. Much work has been done to nd ways to dehydrate magnesium chloride without hydrolyzing the material.

This invention provides means of dehydrating magnesium chloride particles or powder, to remove at least a substantial portion of the water content thereof, to provide, at the same time, molten magnesium chloride ready to be fed either directly or with further processing to an electrolytic cell for the production or magnesium metal and chlorine.

It is therefore a general object of this invention to provide a means of dehydrating magnesium chloride.

Another object of the invention is to provide a method of dehydrating magnesium chloride in an arrangement wherein the magnesium chloride is melted and thereby made ready for introduction into an electrolytic cell for the production of magnesium metal and chlorine.

These general objects, as well as more specific objects of the invention, will be understood by reference to the following description and claims, taken in conjunction with the drawings.

DESCRIPTION OF THE VIEWS FIG. l is a cross-sectional view of an apparatus for practicing the method of this invention.

FIG. 2 is a cross-sectional view taken along the line line 2 2 of FIG. 1 showing the launder and hood portions of the apparatus as used in practicing the method of this invention.

FIG. 3 is a cross-sectional view taken along the lines 3-3 of FIG. l, with the hood not shown, and showing 3,564,722 Patented Feb. 23, 1971 one arrangement of introducing the discharge from the launder into a venturi.

DETAILED DESCRIPTION Referring now to the drawings and first to FIG. l, an apparatus for practicing the method of this invention is shown. A pot furnace 10 is provided containing a quantity of melt 12. The furnace 10 is heated, such as by means of gas burner 14 having a combustion mixture supplied through pipe 16. Furnace 10 may be heated electrically. While in the drawing the gas burner 14 is shown in a separate compartment below the melt 12, the burner may be submersed in direct contact with the melt.

By means of a pump 18 driven by `drive shaft 20, which in turn is driven by a motor 22, the melt is pumped through conduit 24 and is discharged onto a launder 26. In the launder 26 a relatively shallow stream 28 of melt flows by gravity along the length of the launder and is discharged at the lower end 30.

Melt 12 is composed of fused salts. 'The exact composition of melt 12 depends upon the use to which the melt is put. When the melt is to be used in an electrolytic cell for the production of magnesium and chlorine, the composition of the melt will be determined by the specific i process utilized for the operation of the cell.

Magnesium chloride powder 32 is spread onto a conveyor belt 34 and from there is discharged onto the surface of stream 28 in the launder 26. Powder 32 may be derived from any source, such as a spray dryer, uid bed dryer, shelf dryer, or so forth. Magnesium chloride powder 32 is normally substantially free of water but nevertheless the product of most spray drying processes, or other drying processes, even the most efficient, contains some residual water. It is an object of this invention to remove all or at least a substantial portion of the water remaining in the powdered magnesium chloride product 32.

The magnesium chloride powder 32 may be discharged onto the surface of stream 28 in a variety of ways, such as by means of a vibrating feeder, a screen feeder, conveyor arrangement, or distribution plate 34 as illustrated. The function of distribution plate 34 is to spread the magnesium chloride powder 32 evenly on the surface of stream 28.

Covering the launder 26 is a fume hood 36, having an outlet 38. The outlet 38 connects to an off gas discharge arrangement for venting to the atmosphere. In the typical installation the off gas will be treated before venting to the atmosphere although such treating arrangement is not a portion of this invention.

In the preferred arrangement a fan or blower intake will be connected to outlet opening 38 so that gas driven off the powdered magnesium chloride is drawn quickly away from the molten streams 28. The discharge end 30 of the launder 26 is positioned about a mixing device 40 which, in FIG. l, is illustrated by a venturi. The lowerend of venturi 40 communicates with the closed pot furnace 10. The molten stream 28 and the magnesium chloride powder 32 are discharged into the venturi 40. The natural flow effects of the venturi causes a rapid mixing of the magnesium chloride powder and the melt stream to achieve a rapid mixing and melting of the powder.

The mixing device 40 may be of any type which achieves a rapid mixing of the powder and melt stream as they pass downwardly into furnace pot 10, and may include mechanical mixers having moving agitator elements.

The melt product is taken ofi through outlet 42 and may be passed directly to an electrolytic cell for processing to produce magnesium metal and chlorine, or the melt, may be otherwise utilized as desired.

FIG. 2 shows a typical cross-sectional view of the launder 26 which is more 0r less in the nature of a flat gradually declining trough. The fume hood 36 closes substantially all of the upper surface of the launder 26 to remove the off gas.

FIG. 3 shows an arrangement of the invention wherein the venturi 40 is of circular cross section throughout and in which the launder 26 is tapered at the discharge end 30 to discharge into the venturi.

An alternate arrangement includes the utilization of a Venturi having a rectangular cross-sectional configuration and `having a rectangular throat in which event the launder 26 would not need a tapered discharge end 30 as shown in FIG. 3.

METHOD OF OPERATION In the operation of the invention fused salt is heated in furnace 10. The melt is anhydrous, or at least as free of water as is economically possible to obtain. In the preferred arrangement the melt should be at approximately 1200 to 1500 F. as it is discharged through conduit 24 onto launder 26. At this temperature any water content in the magnesium chloride powder 32 discharged onto the stream will immediately flash off. The secret of the process is being able to bring the temperature of the powder up sufficiently high to Hash off the water and withdraw the water in the form of steam quickly enough to prevent substantial hydrolyzation of the magnesium chloride. When magnesium chloride hydrolyzes the product contains magnesium oxide and hydrochloric acid. The magnesium oxide or its intermediate magnesium oxychloride is deleterious to electrolytic cells. While a small percentage of magnesium oxide may be tolerated in electrolytic cells, too much results in a great reduction in efficiency of the cells and a level is soon reached at which it is not commercially profitable to produce magnesium metal.

The magnesium chloride powder 32, with substantially all of the water having been evaporated therefrom, remains essentially on the surface of the stream 38 as it ows downwardly in the launder 26 until it reaches the discharge end 30. The molten and powdered material are discharged into mixing venturi 30 and passed through the venturi throat 44 where the natural venturi flow action causes rapid mixing of the two materials, melting the magnesium chloride powder. Thus as the material is discharged from the venturi 30 into furnace pot 10 it is essentially in the molten state. Any remaining solid magnesium chloride will be rapidly melted within the furnace.

Thus, the magnesium chloride powder 32 is converted by the process into substantially anhydrous molten magnesium chloride for conveyance by way of outlet conduit 42 to an electrolytic cell for processing or for such further treatment or processing as may be desired. The water flashed off the magnesium chloride powder 32 on the surface of the stream in launder 26 is accumulated in the fume hood 36 and drawn off through outlet 38. The gases or fumes withdrawn through outlet 38 are primarily water vapor with a small amount of hydrochloric acid resulting from a small amount of hydrolysis action which inadvertently takes place.

While the invention has been described as it relates to dehydrating magnesium chloride it can be seen that the invention is equally applicable to the treatment of mixtures of chlorides. The term powder herein refers to magnesium chlorides, or mixtures containing magnesium chloride, in solid particulate form, irrespective of particle size or shape.

While the invention has been described with a great deal of particularity it is manifest that many changes may be made in the details of construction, the arrangement of components, and the sequence and arrangement of steps in the method of this invention without departing from the spirit and scope thereof.

What is claimed:

1. A method of dehydrating magnesium chloride powder containing some water comprising the steps of:

flowing a melt in a shallow exposed surface stream;

introducing onto the surface of the owing stream at one end magnesium chloride powder containing some water, at least a substantial portion of such water being flashed olf as steam by the heat of the flowing stream;

withdrawing the steam away from the owing stream;

and

mixing the magnesium chloride powder floating on the stream with the stream at the other end to melt the powder.

What is claimed:

2. A method of dehydrating magnesium chloride powder containing some water according to claim I wherein the step of mixing floating powder with the stream includes passing the stream having floating powder thereon downwardly through a mixing device.

3. A method of dehydrating magnesium chloride powder containing some water according to claim 2 Wherein said mixing device is a venturi.

4. A method of dehydrating magnesium chloride powder containing some water according to claim 1 wherein the stream has a temperature of approximately 1200 to 1500 F.

5. A method of dehydrating magnesium chloride powder according to claim 1 wherein said melt is fused salts.

6. A method of dehydrating magnesium chloride particles having some water to provide molten anhydrous magnesium chloride such as for use as cell feed comprising:

maintaining a molten bath of fused salts;

pumping molten fused salts from the bath through a conduit to an elevation higher than the molten bath; discharging the molten fused salts onto a launder to provide a flowing melt in a shallow exposed surface stream;

introducing onto the surface of the flowing stream magnesium chloride powder containing some water, at least a substantial portion of the water being flashed off as steam;

withdrawing the steam away from the flowing stream;

mixing the floating powder on the stream with the stream to melt the powder;

discharging the stream into the molten bath; and

withdrawing melt from the bath as required.

7. A method of dehydrating magnesium chloride powder containing some water according to claim 6 wherein the step of mixing floating powder with the stream includes passing the stream having floating powder thereon as the stream leaves the launder downwardly through ka mixing device.

8. A method of dehydrating magnesium chloride powder containing some water according to claim 7 wherein said mixing device includes a venturi.

9. A method of dehydrating magnesium chloride powder containing some water according to claim 6 wherein the stream of fused salts has a temperature of approximately 1200 to 1500 F.

10. Apparatus for dehydrating magnesium chloride powder containing some water, comprising:

a closed furnace in which a melt of fused salts is maintained; launder positioned at an elevation above said furnace, the launder having an input end and a discharge end;

a pump means having connection to said furnace providing a llow of molten fused salts;

a conduit connectig at one end with said pump means and at the opposite end with said launder input end whereby an exposed surface stream of molten fused salts is provided in said launder;

a feeder positioned to continuously discharge at a predetermined rate magnesium chloride powder having some Water onto the surface of the stream of molten fused salts in said launder, at least a substantial portion of the water contained in said powder being flashed off the stream surface as steam by the heat of the flowing stream;

fume hood covering said launder having means of 'withdrawing steam away from said flowing steam; and

mixing member having an upper intake end and a lower discharge end, the upper end being positioned below the discharge end of said launder and the discharge end communicating with said furnace, the stream of molten fused salts passing from said launder downwardly through said mixing device into said 5 powder according to claim 10 wherein said mixing device is a venturi.

References Cited UNITED STATES PATENTS 12/ 1924 Prichard et al 34-9 5/1935 Williams 34-9 JOHN I. CAMBY, Primary Examiner 

